Purification of molten metal



Patented Aug. 21,1934

1,971,149 [PURIFICATION OF MOLTEN METAL William F. Zimmerli, Niagara Falls, N. Y., as-

signor to E. I. du Pont de Nemours & Company, Incorporated, Wilmington, Del., a corporation of Delaware No Drawing, Application September 12, 1932,,

Serial No. 632,794

3 Claims. (01. 75-452) FFICE This invention relates to the purification of metals or alloys, particularly to the treatment of molten iron, steel, copper, brass or the like with sodium cyanide or other metal cyanides or 5 equivalent cyanogen derivatives.

In the manufacture andpurification of such metals and alloys, considerable difficulty is experienced, due to the partial oxidation of the metal, resulting in the occlusion of oxides which detract from the desirable physical properties of the product. This difficulty is partially corrected by the addition of deoxidizing agents which reduce these oxides. The present treating materials do not give entirely satisfactory results in many cases because they either form oxides of other metals in the melts, or because an excess of the treating material itself adversely affects the quality of the product. Thus, aluminum has been found to be an eflicient medium'in reducing iron oxide in molten steel, but the aluminum oxide itselfis largely occluded in the final product. While the steel is improved, it would be more desirable to reduce the iron oxide by some other method which would not leave an undesirable residue. case of copper it has been found-that calcium is an effective deoxidizing material, but an excess of calcium remaining in the copper reduces the electrical conductivity. In the treatment of brass, bronze, and copper the element, phosphor us, is commonly used in the form of its copper alloy, but in many cases an excess of this in the alloy is objectionable.

The object of this invention is to provide a satisfactory treating means and material for such molten metals which will not leave these objectionable residues in the product to detract from desirable physical properties. I have found that these results can be secured by the treatment of the molten metal with a cyanogen compound, and more specifically a cyanogen salt such as a metal cyanide, cyanate, thiocyanate, or other cyanogen derivatives. Such metal cyanides as sodium cyanide, copper cyanide or the like can be used. Thus, copper cyanide can be used for the treatment of copper and the final reaction product remaining in the metal In the nates eventually transform to carbonates. At the temperature of molten steel, for example, with very small amounts of reducible oxide, the products formed would probably vary considerably; however, iron oxide would be reduced, and the cyanide would leave an alkali compound which would be easily fusible so that it would come out of the molten metal as a slag. Other impurities, such as occluded oxide silicon, manganese, and other metals taken up from the linings of the furnaces, slags, etc., or produced by the additions of the elements to effect deoxidation or desulphurization, would either be reduced or converted to fusible slags easily removable from the metals.

. As noted above, metal cyanides of the constituents of the final product would be preferable in cases where small amounts of foreign elements would-give lower quality products. Thus, as noted above, copper can be deoxidized with pure copper cyanide, so that the final reaction product remaining in the metal is pure copper. If the copper were first deoxidized with calcium, an excess of this can be removed by adding copper cyanide.

After treatment of the molten metal with cyanide carrying material, it may be advantageous to treat the metal with a degasifying agent. For this purpose any of the common degasifiers suited for this particular metal may be used.

I have in this manner treated molten steel with sodium cyanide, and molten copper with sodium cyanide and copper cyanide; molten copper has also been treated with sodium cyanide followed by a 30% alloy of calcium and copper as a degasifier. Other degasifiers can be used to eliminate blow-holes which might be caused by occluded gases.

.In the treatment of steel with sodium cyanide, the procedure was in general to drop broken pieces of sodium cyanide, preferably contained in paper envelopes, into the ladle and then immediately pour the molten steel from a large ladle over this cyanide. There was no violent spattering reaction, but on contact of the molten metal with the cyanide, dense white fumes are developed which subside in a short time; this is followed by an evolution of gases from the metal. The metal is held until the evolution of gases from the molten metal has ceased, whereupon the metal is cast.

The treatment of copper with cyanide materials has been carried out in several ways. In the first place, molten copper has been poured over sodium cyanide. Secondly, it has been poured over copper cyanide; and finally, the

cyanide materials have been added to the molten copper. Either of the methods is satisfactory. For example, three ounces of 96-98% sodium cyanide lumps were added to 150 lbs. of molten copper. The cyanide was first placed in a graphite phosphorizer which had small holes bored through the top of the cup to assist in assuring contact of molten sodium cyanide-with the copper. melt. Sodium cyanide was added just before pouring the metal and suflicient time allowed for'the generated gases to boil out- The flux, consisting of lime and sodium-borate as a slag, was left on the copper during the treatment with sodium cyanide. Copper has been treated when melted in a reducing atmosphere, keeping the crucible covered; andalso inan oxidizing atmosphere. No difficulty was experienced with the introduction of the sodium cyanide into the copper. The castingsobtained showed conductivities much better than the conductivity of the untreated copper.

Further, copper which has thus been treated with sodium cyanide, was degasifled by means of a 30% alloy of calcium and copper; thisresulted in castings having a very high conductivity.

I claim:

1. Method 01' improving the properties of copper or its alloys which. comprises treating said copper or alloys thereof in the molten state with copper cyanide.

2. Method of improving the properties of copper or its alloys which comprises treating said copper or alloys thereof in the molten state with copper cyanide and thereafter degasirying the melt.

3. Method of improving the properties of copper or its alloys which comprises treating said copper or alloys thereof in the molten state with copper cyanide and thereafter degasifying the melt with a copper-calcium alloy.

WIILIAM F. ZIMIMERIJ. 

